How many people can ride a single mount of their the appropriate size?

Just wondering, are there any rules for multiple people riding a single mount. Realistically, two people can fit on a single horse. Is there anything in the rules that says there is a penalty for doing so? So long as they don't go over the horse's weight capacity, what different would it be if it was just one heavy person. If I recall correctly, I think this was actually a viable tactic some army used, "The person the back was an archer." or just for the sake of how many people can travel on horse back when traveling.

I can see actual room being an issue, but I can't see anything that says you can't do this. Nor do I see any penalties for doing so.

Just wondering, are there any rules for multiple people riding a single mount. Realistically, two people can fit on a single horse. Is there anything in the rules that says there is a penalty for doing so? So long as they don't go over the horse's weight capacity, what different would it be if it was just one heavy person. If I recall correctly, I think this was actually a viable tactic some army used, "The person the back was an archer." or just for the sake of how many people can travel on horse back when traveling.

I can see actual room being an issue, but I can't see anything that says you can't do this. Nor do I see any penalties for doing so.

I rule it as if the riders are squeezing. You can certainly ride two to a Horse (standard example), but once combat starts things get wonky.

If I recall correctly, I think this was actually a viable tactic some army used, "The person the back was an archer." or just for the sake of how many people can travel on horse back when traveling.

It's been reasonably common with camels and standard practice with elephants. I don't recall anyone making this work with horses, though. I wouldn't base it on the mount's size, but specify it for each creature. Treating two people on a horse as squeezing sounds pretty good.

Don't forget to calculate the mount's load as well.

Just wondering, are there any rules for multiple people riding a single mount. Realistically, two people can fit on a single horse. ...

My guess would be 2^size-class-difference is a max.

A human can ride a human piggy back.

Two people can ride a horse.

Four people can ride an elephant.

Eight people can probably ride a Dragon/giant.

The limits would be encumbrance and saddling. For instance, you could get four gnomes on a horse if the horse had a palanquin style saddle (as in 4 people on an elephant).

So without a saddle it'd get reduced to 2^(size-class difference - 1).

After all, it's not so much a matter of how many pixies you could fit on the back of a leviathan, as it is a question of where they would sit...

The more encumbered the animal, the greater the minuses would be on the _riders_ as they are crowded and the animal is acting "atypically" due to the loading.

[Disclaimer: this isn't Pathfinder per-se; It's general observations of real life as have been applied in prior gaming groups I've played with, in other rules systems, projected into Pathfinder... if you get my drift.]